Multilayered polyolefin films, methods of manufacture thereof and articles comprising the same

ABSTRACT

Disclosed herein is a multilayer film comprising two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer. Disclosed herein is a method comprising coextruding a multilayered film comprising two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer; and coextruding the multilayered blown film.

BACKGROUND

This disclosure relates to multilayered polyolefin films, methods of manufacture thereof and to articles comprising the same.

Multilayered films are widely used as heavy duty shipping sacks for bagging bulk products such as chemicals, polymers, fertilizers and animal food. These multilayers are often polyethylene based, combining high density polyethylene (HDPE) as stiffening layer and metallocene linear low density polyethylene (LLDPE) sealant layer for sealability and toughness. Combinations of different type of polyethylenes layers and proper layer ratio selection offers desirable properties such as stiffness for mechanical strength and machineability (i.e., bag filling operation), toughness (good machine direction tear and dart drop) and sealability (good heat seal property). For polyethylene based multilayered films, incorporating more HDPE increases stiffness. However, the tear resistance in the machine direction (MD) is reduced. There therefore exists a need for improved high stiffness, high toughness multilayer films and heavy duty packaging in order to reduce the multilayered film thickness.

SUMMARY

Disclosed herein is a multilayer film comprising two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer.

Disclosed herein is a method comprising coextruding a multilayered film comprising two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer; and blowing the multilayered film.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an exemplary embodiment of the multilayered film; and

FIG. 2 depicts an exemplary embodiment of a multilayered film that comprises two multilayered films of the FIG. 1 that are coextruded or laminated together.

DETAILED DESCRIPTION

“Composition” and like terms mean a mixture of two or more materials, such as a polymer which is blended with other polymers or which contains additives, fillers, or the like. Included in compositions are pre-reaction, reaction and post-reaction mixtures the latter of which will include reaction products and by-products as well as unreacted components of the reaction mixture and decomposition products, if any, formed from the one or more components of the pre-reaction or reaction mixture.

“Blend”, “polymer blend” and like terms mean a composition of two or more polymers. Such a blend may or may not be miscible. Such a blend may or may not be phase separated. Such a blend may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art. Blends are not laminates, but one or more layers of a laminate may contain a blend.

“Polymer” means a compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer, usually employed to refer to polymers prepared from only one type of monomer, and the term interpolymer as defined below. It also embraces all forms of interpolymers, e.g., random, block, etc. The terms “ethylene/a-olefin polymer” and “propylene/a-olefin polymer” are indicative of interpolymers as described below. It is noted that although a polymer is often referred to as being “made of” monomers, “based on” a specified monomer or monomer type, “containing” a specified monomer content, or the like, this is obviously understood to be referring to the polymerized remnant of the specified monomer and not to the unpolymerized species.

“Interpolymer” means a polymer prepared by the polymerization of at least two different monomers. This generic term includes copolymers, usually employed to refer to polymers prepared from two or more different monomers, and includes polymers prepared from more than two different monomers, e.g., terpolymers, tetrapolymers, etc.

“Polyolefin”, “polyolefin polymer”, “polyolefin resin” and like terms mean a polymer produced from a simple olefin (also called an alkene with the general formula C_(n)H_(2n)) as a monomer. Polyethylene is produced by polymerizing ethylene with or without one or more comonomers, polypropylene by polymerizing propylene with or without one or more comonomers, etc. Thus, polyolefins include interpolymers such as ethylene-α-olefin copolymers, propylene-α-olefin copolymers, etc.

“Melting Point” as used here (also referred to a melting peak in reference to the shape of the plotted DSC curve) is typically measured by the DSC (Differential Scanning calorimetry) technique for measuring the melting points or peaks of polyolefins as described in U.S. Pat. No. 5,783,638. It should be noted that many blends comprising two or more polyolefins will have more than one melting point or peak; many individual polyolefins will comprise only one melting point or peak.

The term ‘and/or” includes both “and” as well as “or”. For example, the term A and/or B is construed to mean A, B or A and B.

Disclosed herein is a multilayered film that comprises a plurality of layers and that can be used as heavy duty shipping sacks for bagging a variety of different bulk products. The multilayer film comprises at least five layers—a first layer or an outer layer that comprises polyethylene, a second layer, which is a tie layer that comprises a diblock polymer, a third layer (also called a core layer) that comprises polypropylene, a fourth layer, which is also a tie layer that comprises a diblock polymer, and a fifth layer (also an outer layer that is opposedly disposed to the first layer) that comprises polyethylene. The presence of a core layer that comprises polypropylene in the multilayered film provides it with improved stiffness, high creep resistance, high temperature performance and oil/crease resistance, which enables the multilayered film to be used for bagging and shipping large masses of material or products. In another exemplary embodiment, the core layer has a thickness that is less than 20% of the thickness of the multilayered film.

FIG. 1 depicts the multilayered film 100 that comprises the first layer or outer layer 102, the second layer or tie layer 104, the third layer or core layer 106, the tie layer 108 and the fifth layer 110. In one embodiment, the multilayered film 100 has a symmetrical structure about a center line drawn through the length of the film. While the FIG. 1 depicts a single 5-layered multilayered film, commercial embodiments of the film can include multiples of the 5-layered multilayered film. For example, a single multilayered film can contain 2 or more 5-layered multilayered films that contact each other. In one embodiment, a single multilayered film can have 2 to 10 5-layered multilayered films, specifically 2 to 8 multilayered films, and more specifically 2 to 5 multilayered films that contact each other. In an exemplary embodiment, the plurality of multilayered films are coextruded. In another exemplary embodiment, the plurality of multilayered films are bonded together using an adhesive layer.

As may be seen in the FIG. 1, the first layer 102 and the fifth layer 110 are outer layers or skin layers that are disposed at opposing ends of the multilayered film and comprise a polyethylene. The following description will refer to the first layer 102 and the fifth layer 110 collectively as outer layers. The polyethylene is selected from ultralow density polyethylene (ULDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), high melt strength high density polyethylene (HMS-HDPE), ultrahigh density polyethylene (UHDPE), and combinations thereof. In a further embodiment, the polyethylene has a density greater than 0.950 g/cc (i.e., a HDPE). The combinations can include blends, copolymers and blends of copolymers. In an exemplary embodiment, the polyethylene used in the outer layers is a linear low density polyethylene, an ethylene-α-olefin copolymer, or a combination thereof. When the outer layers comprise a linear low density polyethylene, an ethylene-α-olefin copolymer, or a combination thereof, they may also optionally contain a LDPE and/or HDPE.

In an exemplary embodiment, the outer layers 102 and 110 comprise linear low density polyethylene (LLDPE). LLDPE is a copolymer (also referred to as an interpolymer) of ethylene and an α-olefin having 3 to 12 carbon atoms, specifically 4 to 8 carbon atoms (e.g., propene, 1 butene, 4-methyl-1-pentene, 1-hexene, 1 octene, 1-decene, and the like), that has sufficient α-olefin content to reduce the density of the copolymer to that of LDPE. The term “LLDPE”, includes both—resin manufactured using the traditional Ziegler-Natta catalyst systems as well as single-site catalysts such as metallocenes (sometimes referred to as “m-LLDPE”). LLDPEs contain less long chain branching than LDPEs and includes the substantially linear ethylene polymers which are further defined in U.S. Pat. No. 5,272,236, U.S. Pat. No. 5,278,272, U.S. Pat. No. 5,582,923 and U.S. Pat. No. 5,733,155; the homogeneously branched linear ethylene polymer compositions such as those in U.S. Pat. No. 3,645,992; the heterogeneously branched ethylene polymers such as those prepared according to the processes disclosed in U.S. Pat. No. 4,076,698; and/or blends thereof (such as those disclosed in U.S. Pat. No. 3,914,342 or U.S. Pat. No. 5,854,045). The LLDPE can be made by any process such as gas phase polymerization, solution phase polymerization, slurry polymerization or combinations thereof.

In one embodiment, the LLDPE used in the outer layers 102 and 100 comprises the linear low density polyethylene having a melt index I₂ of 0.25 to 2.5 g/10 minutes when measured as per ASTM D 1238 at 190° C. and 2.16 kg. An exemplary LLDPE for use in the outer layers 102 and 110 is ELITE™ 5100, which is an ethylene-octene copolymer with melt index of 0.85 g/10 min (measured as per ASTM D1238 at 190° C. and 2.16 kg), density 0.920 g/cc (measured as per ASTM D 792), polydispersity index (PDI) Mw/Mn=3.45 and Mw=130,300 grams per mole, and commercially available from The Dow Chemical Company. Other exemplary LLDPE's that can be used in the outer layers 102 and 110 are linear ethylene-based polymers such as DOWLEX™ Polyethylene Resins, ELITE™ and ELITE AT™ brand enhanced polyethylene resin, all available from The Dow Chemical Company, and EXCEED™ metallocene polyethylenes, available from ExxonMobil Chemical Company.

Another exemplary polyethylene for use in the outer layers is homogeneously branched ethylene-α-olefin copolymers. These copolymers can be made with a single-site catalyst such as a metallocene catalyst or constrained geometry catalyst, and typically have a melting point of less than 105, specifically less than 90, more specifically less than 85, even more specifically less than 80 and still more specifically less than 75° C. The melting point is measured by differential scanning calorimetry (DSC) as described, for example, in U.S. Pat. No. 5,783,638. The α-olefin is preferably a C₃₋₂₀ linear, branched or cyclic α-olefin. Examples of C₃₋₂₀ α-olefins include propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. The α-olefins can also contain a cyclic structure such as cyclohexane or cyclopentane, resulting in an α-olefin such as 3-cyclohexyl-1-propene (allyl cyclohexane) and vinyl cyclohexane.

Illustrative homogeneously branched ethylene-α-olefin copolymers include ethylene/propylene, ethylene/butene, ethylene/l-hexene, ethylene/l-octene, ethylene/styrene, and the like. Illustrative terpolymers include ethylene/propylene/l-octene, ethylene/propylene/butene, ethylene/butene/1-octene, and ethylene/butene/styrene. The copolymers can be random copolymers or block copolymers.

Examples of commercially available homogeneously branched ethylene-α-olefin interpolymers useful in the outer layers 102 and 110 include homogeneously branched, linear ethylene-α-olefin copolymers (e.g. TAFMER® by Mitsui Petrochemicals Company Limited and EXACT® by Exxon Chemical Company), and the homogeneously branched, substantially linear ethylene-α-olefin polymers (e.g., AFFINITY™ and ENGAGE™ polyethylene available from the Dow Chemical Company). Blends of any of these interpolymers can also be used in the outer layers 102 and 110. An exemplary ethylene-α-olefin copolymer that may be used in the outer layers 102 and 110 is AFFINITY PL1880G, commercially available from the Dow Chemical Company.

Low density polyethylene (LDPE) may also be used in the outer layers 102 and 110. The term “LDPE” may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene” and is defined to mean that the polymer is partly or entirely homopolymerized or copolymerized in autoclave or tubular reactors at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides. LDPE and the methods of manufacturing LDPE are described in U.S. Pat. No. 4,599,392, incorporated herein in its entirety by reference.

The preferred LDPE for use in the outer layers 102 and 110 has a density in the range of from 0.915 to 0.930 g/cm³ and a melt index of from 0.1 to 2.5 g/10 min, preferably less than or equal to 1 g/10 min.

High density polyethylene (HDPE) can also be used in the outer layers 102 and 110. The term “HDPE” refers to polyethylenes having densities greater than about 0.940 g/cm3, which are generally prepared with Ziegler-Natta catalysts, chrome catalysts or even metallocene catalysts. The HDPE has a melt index of from 0.4 to 2.5 g/10 min.

In one embodiment, the outer layers 102 and 110 can comprise a blend of LLDPE and LDPE, LLDPE and HDPE or a combination of LLDPE with LDPE and HDPE. When the outer layer comprise LLDPE with LDPE and/or HDPE, the LLDPE is used in an amount of 25 to 95 wt %, specifically 40 to 90 wt %, based on the total weight of the outer layer. The LDPE and/or HDPE may be used in amounts of 5 to 75 wt %, specifically 10 to 60 wt %, based on the total weight of the outer layer.

Each of the outer layers 102 and 110 has a thickness of 20 to 44%, specifically 30 to 40%, of the total thickness of the multilayer film 100.

The tie layers 104 and 108 are disposed on opposing sides of the third layer 106. With reference to the FIG. 1, each tie layer 104 and 108 has a first face and a second face that are on opposite sides of the tie layer. The tie layer 104 has a first face 103 that contacts the outer layer 102 and a second face 105 (that is opposedly disposed to the first face 103) that contacts the core layer 106. The tie layer 108 has a first face 109 that contacts the outer layer 110 and a second face 107 (that is opposedly disposed to the first face 109) that contacts the core layer 106. The tie layers 104 and 108 are operative to bond the outer layers 102 and 110 respectively to the core layer 106.

The tie layers 104 and 108 each comprise a crystalline block copolymer composite. In addition to the crystalline block copolymer composite, the tie layers 104 and 108 can optionally comprise either an ethylene-α-olefin copolymer or a polyolefin that comprises polypropylene and polyethylene.

Each of the tie layers comprises a crystalline block copolymer composite (CBC). The term “crystalline block composite” (CBC) refers to polymers having three components: a crystalline ethylene based polymer (CEP) (also referred to herein as a soft polymer), a crystalline alpha-olefin based polymer (CAOP) (also referred to herein as a hard polymer), and a block copolymer comprising a crystalline ethylene block (CEB) and a crystalline alpha-olefin block (CAOB), wherein the CEB of the block copolymer is the same composition as the CEP in the block composite and the CAOB of the block copolymer is the same composition as the CAOP of the block composite. Additionally, the compositional split between the amount of CEP and CAOP will be essentially the same as that between the corresponding blocks in the block copolymer. When produced in a continuous process, the crystalline block composites desirably have a polydispersity index (PDI) from 1.7 to 15, specifically 1.8 to 10, specifically from 1.8 to 5, more specifically from 1.8 to 3.5. Such crystalline block composites are described in, for example, US Patent Application Publication Nos. 2011/0313106, 2011/0313108 and 2011/0313108, all published on Dec. 22, 2011, incorporated herein by reference with respect to descriptions of the crystalline block composites, processes to make them and methods of analyzing them.

CAOB refers to highly crystalline blocks of polymerized alpha olefin units in which the monomer is present in an amount greater than 90 mol percent, specifically greater than 93 mol percent, more specifically greater than 95 mol percent, and specifically greater than 96 mol percent. In other words, the comonomer content in the CAOBs is less than 10 mol percent, and specifically less than 7 mol percent, and more specifically less than 5 mol percent, and most specifically less than 4 mol %. CAOBs with propylene crystallinity have corresponding melting points that are 80° C. and above, specifically 100° C. and above, more specifically 115° C. and above, and most specifically 120° C. and above. In some embodiments, the CAOB comprise all or substantially all propylene units. CEB, on the other hand, refers to blocks of polymerized ethylene units in which the comonomer content is 10 mol % or less, specifically between 0 mol % and 10 mol %, more specifically between 0 mol % and 7 mol % and most specifically between 0 mol % and 5 mol %. Such CEB have corresponding melting points that are specifically 75° C. and above, more specifically 90° C., and 100° C. and above.

In one embodiment, the crystalline block composite polymers comprise propylene, 1-butene or 4-methyl-1-pentene and one or more comonomers. Specifically, the block composites comprise in polymerized form propylene and ethylene and/or one or more C₄₋₂₀ α-olefin comonomers, and/or one or more additional copolymerizable comonomers or they comprise 4-methyl-1-pentene and ethylene and/or one or more C₄₋₂₀ α-olefin comonomers, or they comprise 1-butene and ethylene, propylene and/or one or more C₅-C₂₀ α-olefin comonomers and/or one or more additional copolymerizable comonomers. Additional suitable comonomers are selected from diolefins, cyclic olefins, and cyclic diolefins, halogenated vinyl compounds, and vinylidene aromatic compounds. Preferably, the monomer is propylene and the comonomer is ethylene.

Comonomer content in the crystalline block composite polymers may be measured using any suitable technique, with techniques based on nuclear magnetic resonance (NMR) spectroscopy preferred.

The block composites and crystalline block composites have a melting point Tm greater than 100° C. specifically greater than 120° C., and more specifically greater than 125° C. In an embodiment, the Tm is in the range of from 100° C. to 250° C., more specifically from 120° C. to 220° C. and also specifically in the range of from 125° C. to 220° C. Specifically the melt flow ratio (MFR) of the block composites and crystalline block composites is from 0.1 to 1000 dg/min, more specifically from 0.1 to 50 dg/min and more specifically from 0.1 to 30 dg/min.

In an embodiment, the block composites and crystalline block composites have a weight average molecular weight (Mw) from 10,000 to about 2,500,000 grams per mole (g/mole), specifically from 35000 to about 1,000,000 and more specifically from 50,000 to about 300,000, specifically from 50,000 to about 200,000 g/mole.

The crystalline block composite polymers comprise 0.5 to 95 wt % soft copolymer, from 0.5 to 95 wt % hard polymer and from 5 to 99 wt % block copolymer. More specifically, the crystalline block composite polymers comprise from 0.5 to 79 wt % soft copolymer, from 0.5 to 79 wt % hard polymer and from 20 to 99 wt % block copolymer and more specifically from 0.5 to 49 wt % soft copolymer, from 0.5 to 49 wt % hard polymer and from 50 to 99 wt % block copolymer. Weight percents are based on total weight of crystalline block composite. The sum of the weight percents of soft copolymer, hard polymer and block copolymer equals 100%.

In an embodiment, the crystalline block composite polymers comprises 0.5 to 95 wt % CEP, from 0.5 to 95 wt % CAOP and from 5 to 99 wt % block copolymer. More specifically, the crystalline block composite polymers comprise 0.5 to 79 wt % CEP, 0.5 to 79 wt % CAOP and 20 to 99 wt % block copolymer and more specifically 0.5 to 49 wt % CEP, 0.5 to 49 wt % CAOP and 50 to 99 wt % block copolymer. Weight percents are based on total weight of crystalline block composite. The sum of the weight percents of CEP, CAOP and block copolymer equals 100%.

In an embodiment, the block copolymers of the crystalline block composite comprise from 5 to 95 weight percent crystalline ethylene blocks (CEB) and 95 to 5 wt percent crystalline alpha-olefin blocks (CAOB). They may comprise 10 wt % to 90 wt % CEB and 90 wt % to 10 wt % CAOB. More specifically, the block copolymers comprise 25 to 75 wt % CEB and 75 to 25 wt % CAOB, and even more specifically comprise 30 to 70 wt % CEB and 70 to 30 wt % CAOB.

In some embodiments, the crystalline block composites have a Crystalline Block Composite Index (CBCI that is greater than zero but less than about 0.4 or from 0.1 to 0.3. In other embodiments, CBCI is greater than 0.4 and up to 1.0. In some embodiments, the CBCI is 0.1 to 0.9, from about 0.1 to about 0.8, from about 0.1 to about 0.7 or from about 0.1 to about 0.6. Additionally, the CBCI can be in the range of from about 0.4 to about 0.7, from about 0.5 to about 0.7, or from about 0.6 to about 0.9. In some embodiments, CBCI is in the range of from about 0.3 to about 0.9, from about 0.3 to about 0.8, or from about 0.3 to about 0.7, from about 0.3 to about 0.6, from about 0.3 to about 0.5, or from about 0.3 to about 0.4. In other embodiments, CBCI is in the range of from about 0.4 to about 1.0, from about 0.5 to about 1.0, or from about 0.6 to about 1.0, from about 0.7 to about 1.0, from about 0.8 to about 1.0, or from about 0.9 to about 1.0.

The tie layers 104 and 108 may also comprise in addition to the crystalline block composite (CBC), an optional elastomer and/or an optional polypropylene or polyethylene. The optional elastomer can be an ethylene-α-olefin copolymer (which is already detailed above), a polyolefin elastomer (e.g., a propylene based elastomer), a vinyl aromatic block copolymer, or the like, or a combination comprising at least one of the foregoing elastomers.

The polyolefin elastomers may also comprise random or block propylene polymers (i.e., polypropylenes). The random polypropylene elastomer typically comprises 90 or more mole percent units derived from propylene. The remainder of the units in the propylene copolymer is derived from units of at least one α-olefin.

The α-olefin component of the propylene copolymer is preferably ethylene (considered an α-olefin for purposes of this invention) or a C₄₋₂₀ linear, branched or cyclic α-olefin. Examples of C₄₋₂₀ α-olefins include 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. The α-olefins also can contain a cyclic structure such as cyclohexane or cyclopentane, resulting in an α-olefin such as 3-cyclohexyl-1-propene (allyl cyclohexane) and vinyl cyclohexane. Although not α-olefins in the classical sense of the term, certain cyclic olefins, such as norbornene and related olefins, particularly 5-ethylidene-2-norbornene, are α-olefins and can be used in place of some or all of the α-olefins described above. Similarly, styrene and its related olefins (for example, α-methylstyrene, and the like) are α-olefins for purposes of this invention. Illustrative random propylene copolymers include but are not limited to propylene/ethylene, propylene/l-butene, propylene/l-hexene, propylene/l-octene, and the like. Illustrative terpolymers include ethylene/propylene/l-octene, ethylene/propylene/l-butene, and ethylene/propylene/diene monomer (EPDM).

In one embodiment the random polypropylene copolymer has a T_(m) greater than 120° C., and/or a heat of fusion greater than 70 J/g (both measured by DSC) and preferably, but not necessarily, made via Ziegler-Natta catalysis.

In another embodiment, the polyolefin elastomer is a propylene-α-olefin interpolymer and is characterized as having substantially isotactic propylene sequences. The propylene-α-olefin interpolymers include propylene-based elastomers (PBE). “Substantially isotactic propylene sequences” means that the sequences have an isotactic triad (mm) measured by ¹³C NMR of greater than 0.85; in the alternative, greater than 0.90; in another alternative, greater than 0.92; and in another alternative, greater than 0.93. Isotactic triads are well-known in the art and are described in, for example, U.S. Pat. No. 5,504,172 and International Publication No. WO 00/01745, which refers to the isotactic sequence in terms of a triad unit in the copolymer molecular chain determined by ¹³C NMR spectra.

The propylene-α-olefin copolymer comprises units derived from propylene and polymeric units derived from one or more α-olefin comonomers. Exemplary comonomers utilized to manufacture the propylene-α-olefin copolymer are C₂ and C₄ to C₁₀ α-olefins; for example, C₂, C₄, C₆ and C₈ α-olefins.

The propylene-α-olefin interpolymer comprises 1 to 40 percent by weight of one or more alpha-olefin comonomers. All individual values and sub-ranges from 1 to 40 weight percent are included herein and disclosed herein. The propylene-α-olefin interpolymer may have a melt flow rate in the range of 0.1 to 500 grams per 10 minutes (g/10 min), measured in accordance with ASTM D-1238 (at 230° C./2.16 Kg). The propylene-α-olefin interpolymer has crystallinity in the range of from at least 1 percent by weight (a heat of fusion (H_(f)) of at least 2 Joules/gram (J/g)) to 30 percent by weight (a H_(f) of less than 50 J/g). The propylene-α-olefin interpolymer has a density of typically less than 0.895 g/cm³. The propylene-α-olefin interpolymer has a melting temperature (T_(m)) of less than 120° C. and a heat of fusion (H_(f)) of less than 70 Joules per gram (J/g) as measured by differential scanning calorimetry (DSC) as described in U.S. Pat. No. 7,199,203. The propylene-α-olefin interpolymer has a molecular weight distribution (MWD), defined as weight average molecular weight divided by number average molecular weight (Mw/Mn) of 3.5 or less; or 3.0 or less; or from 1.8 to 3.0.

Such propylene-α-olefin interpolymers are further described in the U.S. Pat. Nos. 6,960,635 and 6,525,157, the entire contents of which are incorporated herein by reference. Such propylene-α-olefin interpolymers are commercially available from The Dow Chemical Company, under the trade name VERSIFY™, or from ExxonMobil Chemical Company, under the trade name VISTAMAXX™.

The term vinyl aromatic block copolymer means a polymer having at least one block segment of a vinyl aromatic monomer in combination with at least one saturated or unsaturated elastomeric monomer segment, and more preferably not having a block of polymer that is neither elastomeric nor vinyl aromatic. Examples of vinyl aromatic block copolymers are “styrene block copolymer or styrenic block copolymer”. The term ‘styrene block copolymer” or “styrenic block copolymer” means a polymer having at least one block segment of a styrenic monomer in combination with at least one saturated or unsaturated elastomer (rubber) monomer segment, and more preferably not having a block of polymer that is neither rubber or styrenic. Suitable styrene block copolymers having unsaturated rubber monomer units include styrene-butadiene (SB), styrene-isoprene (SI), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), α-methylstyrene-butadiene-α-methylstyrene, α-methylstyrene-isoprene-α-methylstyrene, and the like.

The term “styrene butadiene block copolymer” is used herein inclusive of SB, SBS and higher numbers of blocks of styrene (S) and butadiene (B). Similarly, the term “styrene isoprene block copolymer” is used inclusive of polymers having at least one block of styrene and one of isoprene (I). The structure of the styrene block copolymers can be of the linear or radial type, and of the diblock, triblock or higher block type. In some embodiments, the styrenic block copolymers having at least four different blocks or a pair of two repeating blocks, for example, repeating styrene/butadiene or styrene/ethylene propylene blocks are desirable. Styrene block copolymers are commercially available from Dexco Polymers under the trademark VECTOR®, from KRATON Polymers under the trademark KRATON™, from Chevron Phillips Chemical Co. under the trademark SOLPRENE™ and K-Resin, and from BASF Corp. under the trade designation STYROLUX™. The styrene block copolymers are optionally used singly or in combinations of two or more.

The styrenic portion of the block copolymer is preferably a polymer or interpolymer of styrene or its analogs or homologs, including α-methylstyrene, and ring-substituted styrenes, particularly ring-methylated styrenes. Preferred styrenics are styrene and α-methylstyrene, with styrene being especially preferred.

The elastomer portion of the styrenic block copolymer is optionally either unsaturated or saturated. Block copolymers with unsaturated elastomer monomer units may comprise homopolymers of butadiene or isoprene and copolymers of one or both of these two dienes with a minor amount of styrenic monomer. When the monomer employed is butadiene, it is preferred that between about 35 and about 55 mole percent of the condensed butadiene units in the butadiene polymer block have a 1,2-configuration. When such a block is hydrogenated, the resulting product is, or resembles, a regular copolymer block of ethylene and 1-butene (EB). If the conjugated diene employed is isoprene, the resulting hydrogenated product is or resembles a regular copolymer block of ethylene and propylene (EP). Preferred block copolymers have unsaturated elastomer monomer units, more preferably including at least one segment of a styrenic unit and at least one segment of butadiene or isoprene, with SBS and SIS most preferred. Among these, SIS is preferred because it has been found to be particularly effective to compatibilize polypropylene with other polymers in the composition. Furthermore, it is preferred because of a lower tendency to crosslink forming gels during manufacture as compared to SBS. Styrene butadiene block copolymers are alternatively preferred when a cast tenter line is used in manufacturing a film when its higher clarity and lower haze are advantageous.

Elastomeric styrene block copolymers provide toughness and lower stiffness than would be obtained in the absence of the block copolymer. Elastomeric behavior is indicated by a property of tensile percent elongation at break of advantageously at least about 200, specifically at least about 220, more specifically at least about 240, most specifically at least about 260 and specifically at most about 2000, more specifically at most about 1700, most specifically at most about 1500 percent as measured by the procedures of ASTM D412 and/or ASTM D882. Industrially, most polymers of this type contain 10-80 wt % styrene. Within a specific type and morphology of polymer, as the styrene content increases the elastomeric nature of the block copolymer decreases.

The block copolymers desirably have a melt flow rate (MFR) of at least about 2, specifically at least about 4 grams per 10 minutes (g/10 min), specifically 20 g/10 min, and more specifically 30 g/10 min. Measure MFR according to ASTM method D1238 Condition G.

Preferred styrenic block copolymers include styrene-isoprene-styrene block copolymers (“SIS”), styrene-butadiene-styrene block copolymers (“SBS”), styrene-ethylene-propylene block copolymers (“SEP”), and hydrogenated styrenic block copolymer such as styrene-(ethylene butylene)-styrene block copolymers (“SEBS”) (e.g., the SEBS commercially available from Kraton Polymers LLC under the trade designation KRATON™ 1657). Preferably, the styrenic block copolymer used in the tie layer is SBS.

In one embodiment, the styrene butadiene block copolymer has a radial or star block configuration with polybutadiene at the core and polystyrene at the tips of the arms. Such polymers are referred to herein as star styrene butadiene block copolymers and are within the skill in the art and commercially available from Chevron Phillips Chemical Co. under the trade designation K-Resin. These polymers contain about 27% butadiene or more in a star-block form and often feature a bimodal molecular weight distribution of polystyrene. The inner polybutadiene segments are of about the same molecular weight while the outer polystyrene segments are of different molecular weight. This feature facilitates control of polybutadiene segment thickness, to obtain improved clarity. For high clarity, the polybutadiene segment thickness is preferably about one-tenth of the wavelength of visible spectrum or less.

The ethylene-α-olefin copolymer has been described above as has the polyethylene and will not be detailed again. The polypropylene will be detailed below with reference to the core layer 106.

The CBC can be used in the tie layers in an amount of 100 wt %. When the tie layers 104 and 108 comprise the crystalline block composite (CBC) and the optional elastomer and/or an optional polypropylene or polyethylene, the CBC may be used in amounts of 10 to 90 wt %, specifically 20 to 80 wt %, and more specifically 30 to 70 wt %, based on the total weight of the tie layers 104 and 108. If the elastomer is used, it is present in amounts of up to 50 wt %, specifically 5 to 45 wt %, based on the total weight of the tie layers 104 and 108. If polypropylene and/or polyethylene are used in the tie layers, they can be used either individually or in combination in amounts of up to 50 wt %, specifically 5 to 45 wt %, based on the total weight of the tie layers 104 and 108.

The tie-layers 104 and 108 each have a thickness of 1 to 20%, specifically 2 to 10%, specifically 3 to 8% and more specifically 4 to 6% of the total thickness of the multilayer film.

The core layer 106 comprises polypropylene. It may also optionally comprise an elastomer and polyethylene in addition to the propylene. The polypropylene is selected from random copolymer polypropylene (rcPP), impact copolymer polypropylene (hPP+at least one elastomeric impact modifier) (ICPP) or high impact polypropylene (HIPP), high melt strength polypropylene (HMS-PP), isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), or a combination comprising at least one of the foregoing polypropylenes.

The polypropylene is generally in the isotactic form of homopolymer polypropylene, although other forms of polypropylene can also be used (e.g., syndiotactic or atactic). Polypropylene impact copolymers (e.g., those wherein a secondary copolymerization step reacting ethylene with the propylene is employed) and random copolymers (also reactor modified and usually containing 1.5-7% ethylene copolymerized with the propylene), however, can also be used in the TPO formulations disclosed herein. A complete discussion of various polypropylene polymers is contained in Modern Plastics Encyclopedia/89, mid October 1988 Issue, Volume 65, Number 11, pp. 86-92, the entire disclosure of which is incorporated herein by reference. The molecular weight and hence the melt flow rate of the polypropylene for use in the present invention varies depending upon the application. The melt flow rate for the polypropylene useful herein is generally from about 0.1 grams/10 minutes (g/10 min) to about 100 g/10 min specifically 0.5 g/10 min to about 80 g/10 min, and specifically 4 g/10 min to about 70 g/10 min (measured as per ASTM D1238 at 230° C. and 2.16 kg). The propylene polymer can be a polypropylene homopolymer, or it can be a random copolymer or even an impact copolymer (which already contains a rubber phase). Examples of such propylene polymers include VISTAMAX (made by Exxon Mobil), VERSIFY (made by The Dow Chemical Co.), INSPIRE (made by Braskem), and PROFAX (made by Lyondell).

The core layer 106 may contain polypropylene in an amount of 40 to 100 wt %, specifically 50 to 90 wt %, based on the total weight of the core layer 106.

The core layer 106 may optionally contain an elastomer in an amount of up to 40 wt %, specifically 10 to 35 wt %, based on the total weight of the core. The elastomer can be an ethylene-α-olefin copolymer (which is already detailed above), a polyolefin elastomer (e.g., a propylene based elastomer), a vinyl aromatic block copolymer, or a combination thereof as detailed above. The core layer may also contain polyethylene in an amount of up to 40 wt %, specifically 10 to 35 wt %, based on the total weight of the core. The polyethylenes have been described above, and will not be detailed here again.

The core layer 106 has a thickness of 10 to 40%, specifically 15 to 30%, based on the total thickness of the multilayered film 100. In an exemplary embodiment, the core layer 106 always has a thickness that is less than 20% of the total thickness of the multilayered film 100. Each layer of the multilayer film 100 may contain other additives such as waxes, antioxidants, antiozonants, mold release agents, biocides, thermal stabilizers, pigments, dyes, infrared absorption agents, ultraviolet stabilizers, or the like, or a combination comprising at least one of the foregoing additives.

As noted above, one of more layers of the multilayer can optionally comprise a wax that may reduce the melt viscosity in addition to reducing costs. Non-limiting examples of suitable waxes include petroleum waxes, polyolefin waxes such as low molecular weight polyethylene or polypropylene, synthetic waxes, paraffin and microcrystalline waxes having melting points from about 55 to about 110° C., Fischer-Tropsch waxes, or a combination comprising at least one of the foregoing waxes. In some embodiments, the wax is a low molecular weight polyethylene homopolymer or interpolymer having a number average molecular weight of about 400 to about 6,000 g/mole.

In further embodiments, each of the layers of the multilayer film can optionally comprise an antioxidant or a stabilizer. Non-limiting examples of suitable antioxidants include amine-based antioxidants such as alkyl diphenylamines, phenyl-α-naphthylamine, alkyl or aralkyl substituted phenyl-α-naphthylamine, alkylated p-phenylene diamines, tetramethyl-diaminodiphenylamine and the like; and hindered phenol compounds such as 2,6-di-t-butyl-4-methylphenol; 1,3,5-trimethyl-2,4,6-tris(3′,5′-di-t-butyl-4′-hydroxybenzyl)benzene; tetrakis[(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane (e.g., IRGANOX™ 1010, from Ciba Geigy, New York); octadecyl-3,5-di-t-butyl-4-hydroxycinnamate (e.g., IRGANOX™ 1076, commercially available from Ciba Geigy) and combinations thereof. Where used, the amount of the antioxidant in the composition can be up to about 1 wt %, specifically 0.05 to 0.75 wt %, and specifically 0.1 to 0.5 wt %, based on the total weight of any particular layer.

In further embodiments, the compositions disclosed herein optionally can comprise an UV stabilizer that may prevent or reduce the degradation of the compositions by UV radiation. Non-limiting examples of suitable UV stabilizers include benzophenones, benzotriazoles, aryl esters, oxanilides, acrylic esters, formamidine carbon black, hindered amines, nickel quenchers, hindered amines, phenolic antioxidants, metallic salts, zinc compounds, or the like, or a combination comprising at least one of the foregoing UV stabilizers. Where used, the amount of the UV stabilizer in any particular layer can be from about greater than 0 to about 1 wt %, specifically 0.05 to 0.75 wt %, and specifically 0.1 to 0.5 wt %, based on the total weight of a particular layer.

In further embodiments, the compositions disclosed herein optionally can comprise a colorant or pigment. Any colorant or pigment known to a person of ordinary skill in the art may be used in the adhesion composition disclosed herein. Non-limiting examples of suitable colorants or pigments include inorganic pigments such as titanium dioxide and carbon black, phthalocyanine pigments, and other organic pigments such as IRGAZIN®, CROMOPHTAL®, MONASTRAL®, CINQUASIA®, IRGALITE®, ORASOL®, all of which are available from Ciba Specialty Chemicals, Tarrytown, N.Y. Where used, the amount of the colorant or pigment in any particular layer can be present in an amount of up to 10 wt %, specifically 0.1 to 5 wt %, and more specifically 0.5 to 2 wt %, based on the total weight of any particular layer of the multilayered film.

In one embodiment, in one method of manufacturing the film 100, the respective compositions for each of the layers 102, 104, 106, 108 and 110 of the multilayered film 100 is fed to a separate device in which it is subjected to shear, extensional and elongational forces. The device that exerts the foregoing forces on the composition can be conducted in an extruder (single screw or twin screw), a Henschel mixer, a Waring blender, a Buss Kneader, a Banbury, a roll mill (two or more rolls), high shear impeller disperser, dough mixer, or the like. The ingredients for any layer in the multilayered film may be dry mixed or solution blended in either a Henschel mixer, a Waring blender, a high shear impeller disperser, or the like, prior to being extruded.

In an exemplary embodiment, the composition for each of the respective layers is fed to separate extruders. The composition for the outer layer 102 is fed to a first extruder, the composition for the tie layer 104 is fed to a second extruder, the composition for the core layer 106 is fed to a third extruder, the composition for the tie layer 108 is fed to a fourth extruder and the composition for the outer layer 110 is fed to the fifth extruder. The compositions from the respective extruders are fed to a single die and are coextruded to form the multilayered film. The coextruded film is then blown to form a multilayered film of the desired thickness. In an embodiment, the multilayered film after being coextruded is laminated in a roll mill having two or more rolls.

As detailed above, a plurality of multilayered films may be laminated together to form a single multilayered film. When two or more multilayered films are laminated together, at least one of the common layers may be omitted if desired. For example, if two multilayered films are laminated together as shown in the FIG. 2, then at least one of the outer layers 102 or 110 may be omitted. Thus while a single multilayered film contains 5 layers, two multilayered films laminated together will contain 9 layers, and three multilayered films will contain 13 layers.

The multilayered films disclosed herein are advantageous in that the presence of a core layer that comprises polypropylene in the multilayered film provides it with improved stiffness, high machine direction tear resistance, strong heat seal strength without interlayer delamination, high creep resistance, high temperature performance and oil/crease resistance, which enables the multilayered film to be used for bagging and shipping large masses of material or products.

The multilayered films disclosed herein and the method of manufacturing the films is exemplified in the following examples.

EXAMPLES Example 1

This example demonstrates the disclosed multilayered films and methods of manufacture thereof. These examples were also conducted to demonstrate the properties of the multilayered films over comparative multilayered films.

Dart Drop Impact: This test measures the energy, as a function of mass and drop height, required to cause failure of 50% of the specimens tested. The result is given in grams. Type A darts have heads 1.5 inches in diameter and drop from a height of 26 inches. Type B darts have heads 2 inches in diameter and drop from a height of 60 inches. Specimen failure is defined as any break through the film that can be observed readily by feeling or by viewing under back lighted conditions. Type A and Type B Dart Impact cannot be directly correlated. The test is based upon ASTM STM D 1709.

Elmendorf Tear test: This test is based upon ASTM D 1922. Tear strength is measured using a pendulum impact tester to measure the force required to propagate an existing slit a fixed distance to the edge of the test sample. Fifteen samples are prepared using a specific die cutter. These samples are positioned in the tester and clamped in place. A cutting knife in the tester is used to create a slit in the sample which ends 43 mm from the far edge of the sample. The pendulum is released to propagate the slit through the remaining 43 mm. The energy loss by the pendulum is used to calculate an average tearing force. This test is a Constant Radius test.

Secant Modulus testing: This test, also based upon ASTM D 882, covers the determination of the tensile, or extension, properties of plastics in the form of thin sheeting, including film, which is less than 1 mm (0.04 in) in thickness. Film is defined as having a nominal thickness not greater than 0.25 mm (0.010 in). In this test, the plastic material is pulled until in breaks in order to measure elongation, modulus, tensile yield strength, and tensile strength at break. All specimens are prepared and tested in exactly the same way. For this test, the samples are rectangular and are prepared using a die cutter. For testing tensile strength, the separation speed on the tensile tester is set to 2 in/min. All tests are done on an Instron-type piece of equipment. The secant modulus measurement is a sub-measurement of this test. The modulus is calculated by dividing the tensile stress by the corresponding strain for the linear portion of the curve, or for an extension of the linear line. If there is no linear behavior, a tangent is drawn at the inflection point, to provide toe compensation by using the intersection of the tangent line with the strain axis as zero strain. The secant modulus can then be calculated as the ratio of stress to corrected strain at any point on the curve. Values for secant modulus are reported at 1 and 2% strain.

Tensile Strength: This test, also based upon ASTM D 882, covers the determination of the tensile, or extension, properties of plastics in the form of thin sheeting, including film, which is less than 1 mm (0.04 in) in thickness. Film is defined as having a nominal thickness not greater than 0.25 mm (0.010 in). In this test, the plastic material is pulled until in breaks in order to measure elongation, modulus, tensile yield strength, and tensile strength at break. All specimens are prepared and tested in exactly the same way. For this test, the samples are rectangular and are prepared using a die cutter. For testing tensile strength, the separation speed on the tensile tester is set to 20 in/min. All tests are done on an Instron-type piece of equipment.

Haze test: The total haze of films is measured per ASTM D-1003. A Hazeguard Plus (BYK-Gardner USA; Columbia, Md.) instrument is used to measure the haze. Specimens of 8″×8″ size are used, ensuring there are no wrinkles in the films and an average of at least 5 readings is reported.

Heat Seal test: This work instruction is based upon ASTM Standard Test Method F88, STM for Seal Strength of Flexible Barrier Materials. It measures the force required to separate a test strip of material containing the seal. It also identifies the mode of specimen failure. Specimens are die cut strips that are one inch in width. The test result is a measure of the force required to pull apart the heat seal, or the force required to break the film in cases where the film breaks before the heat seal parts.

The materials used in the various layers of the multilayered film (for this example and for succeeding examples) are detailed in Table 1 below.

TABLE 1 Material Description CBC1 50/50 EP/iPP, 90 wt % C2 in EP, 6.7 melt flow ratio (MFR)* CBC2 50/50 EP/iPP, 90 wt % C2 in EP, 6.8 MFR INSPIRE 114 Impact copolymer polypropylene, 0.5 MFR, Braskem INSPIRE 118 High crystallinity polypropylene, 8.0 MFR, Braskem PP 6D83K Polypropylene random copolymer, 1.9 MFR, Braskem PP H110-02N Polypropylene homopolymer, 2.0 MFR, Braskem ADSTIF High crystallinity polypropylene, 2.3 MFR, HA802H LyondellBasell Industries ELITE 5100G Enhanced Polyethylene Resin, 0.920 g/cm³, 0.85 melt index (MI)**, The Dow Chemical Company ELITE 5400G Enhanced Polyethylene Resin, 0.916 g/cm³, 1.0 MI, The Dow Chemical Company LDPE 133A LDPE, 0.923 g/cm³, 0.25 MI, The Dow Chemical Company AFFINITY Polyolefin plastomer, 0.902 g/cm³, 1.0 MI, The Dow PL1880 Chemical Company ENGAGE 8100 Polyolefin elastomer, 0.870 g/cm³, 1.0 MI, The Dow Chemical Company ENGAGE 8150 Polyolefin elastomer, 0.870 g/cm³, 0.5 MI, The Dow Chemical Company VERSIFY 3000 Propylene-ethylene copolymer, 0.888 g/cm³, 8 MFR, The Dow Chemical Company VERSIFY 2200 Propylene-ethylene copolymer, 0.876 g/cm³, 2 MFR, The Dow Chemical Company *Melt flow rate (MFR): measured as per ASTM D1238 at 230° C. and 2.16 kg **Melt index (MI): measured as per ASTM D1238 at 190° C. and 2.16 kg

The properties for crystalline block copolymer (CBC1) and (CBC2) from Table 1 are shown in the Table 1A.

TABLE 1A Wt % PP Crystalline MFR from Total Tm (° C.) Melt Block (230° C./ HTLC Mw Mw/ Wt % Peak 1 Enthalpy Composite Example 2.16 kg) Separation Kg/mol Mn C₂ (Peak 2) (J/g) Index CBC1 6.7 19.6 114 2.90 48.3 131 (105) 90 0.579 CBC2 6.8 21.3 117 3.14 46.7 128 (105) 88 0.560

Table 2 below shows a series of multilayered films some of which are films that exemplify the invention, while others are comparative films. Comparative film samples are identified with letters (See Samples A-B and D-E), while samples that exemplify the invention are identified with numerals (See Samples 1-5). The core layer 106 comprises Inspire 114. The total film thickness is 5 mils (where 1 mil= 1/1000 of an inch).

TABLE 2 (Outer layers) (Tie layers) 102/104/106/108/110 Layer 102/Layer Layer 104/Layer (Core layers) (percentage of total Sample Structure 110 108 Layer 106 thickness) A 3 Layer ELITE 5100 No tie layer INSPIRE 114 40/20/40 B 5 Layer ELITE 5100 AFFINITY INSPIRE 114 35/5/20/5/35 PL1880G 1 5 Layer ELITE 5100 CBC1 INSPIRE 114 35/5/20/5/35 2 5 Layer ELITE 5100 60% CBC1 + 40% INSPIRE 114 35/5/20/5/35 ENGAGE 8150 3 5 Layer ELITE 5100 60% CBC1 + 20% INSPIRE 114 35/5/20/5/35 ENGAGE 8150 + 20% ELITE 5100 D 3 Layer ELITE 5100 No tie layer INSPIRE 114 37.5/25/37.5 4 5 Layer ELITE 5100 CBC1 INSPIRE 114 32.5/5/25/5/32.5 E 3 Layer ELITE 5100 No tie layer INSPIRE 114 35/30/35 5 5 Layer ELITE 5100 CBC1 INSPIRE 114 30/5/30/5/30

As can be seen in the Table 2, some of the comparative layers have 3 layers (Samples A, D and E). The multilayered films of the invention all have 5 layers. The layers are identified with numerals used in the FIG. 1. The outer layers are referred to by numerals 102 and 110, while the tie layers are referred to by numerals 104 and 108 and the core layer is referred to by numeral 106. Note that the core layer (Layer 106) is 20% of the total multilayer film thickness for Samples A-B and Samples 1-3, 25% for Samples D and 4, and 30% for Samples E and 5.

Inventive samples 1-5 and comparative samples A-B and D-E were manufactured on a LabTech 5-layer blown film line. The diameter of the extrusion die is 75 millimeters (mm) and the die gap is 2 mm. The blow-up ratio (BUR) was 2.4 to 2.5 and lay-flat width 11.4 to 11.6 inch. The nip speed was 10.5 to 12.0 ft/min. The total film thickness was 5 mils (1 mil= 1/1000 of an inch). The line had 5 extruders. For 5-layer structures, extruders 1 and 5 were used for the outer layers (102 and 110), extruders 2 and 4 for tie layers (104 and 108) and extruder 3 for core layer 106. A typical extruder temperature profile is shown in Table 2A. When a blend was used in certain layer, the ingredients were typically dry-blended and fed to the feeder.

TABLE 2A Extruders Zones Temperature (° F.) Extruders 1 and 5: Zone 01 Set point 350 Outer layer Zone 02 Set point 400 Zone 03 Set point 375 Zone 04 Set point 375 Die Set point 420 Extruders 2 to 4: Zone 01 Set point 390 Tie layers and Zone 02 Set point 420 core layer Zone 03 Set point 375 Die Set point 420

The properties of the multilayered films shown in the Table 2 are detailed in the Table 3.

TABLE 3 Dart 1% MD 2% MD MD A Sec Mod Sec Mod tear Heat seal fail Sample (g) (psi) (psi) (g) mode A 832 58896 48507 1400 Delamination B 836 60961 51185 1194 Delamination 1 720 61384 52051 2388 No Delamination 2 808 59917 50888 1588 No Delamination 3 764 54457 47448 1492 No Delamination D 756 64755 54782 980 Delamination 4 560 68993 56651 1952 No Delamination E 700 75032 61460 639 Delamination 5 532 76226 62812 862 No Delamination

From Table 3, it may be seen the inventive Examples 1-3 show improved MD tear and no delamination in the heat seal test when compared with comparative samples A-B. Similarly, compared to Example D, inventive Example 4 has enhanced MD tear and MD modulus without any delamination.

Example 2

In this example, a different core layer 106 is used in the multilayered film as compared with the samples demonstrated in the Example 1. These samples are manufactured in a manner similar to those films of the Example 1. In this example, INSPIRE 118 is used as the core layer 106. The total film thickness is 5 mils. The compositions of the multilayered films are shown in the Table 4 and the properties are shown in the Table 5. Comparative film samples are identified with letters (See Sample F), while samples that exemplify the invention are identified with numerals (See Samples 6-7).

TABLE 4 Layer 102/Layer Layer 104/Layer 102/104/106/108/110 110 108 Layer 106 (percentage of total Sample Structure (Outer layers) (Tie layers) (core layer) thickness) F 3 Layer ELITE 5100 No tie layer INPSIRE 118 40/20/40 6 5 Layer ELITE 5100 CBC1 INPSIRE 118 35/5/20/5/35 7 5 Layer ELITE 5100 CBC1 80% INPSIRE 118 + 35/5/20/5/35 20% ENGAGE 8100

The properties are shown in Table 5.

TABLE 5 Dart 1% MD 2% MD MD A Sec Mod Sec Mod tear Heat seal fail Sample (g) (psi) (psi) (g) mode F 404 80268 68099 802 Delamination 6 500 81705 69324 1921 No Delamination 7 680 72519 60207 2624 No Delamination

Once again, it may be seen that the comparative sample (Sample F) undergoes delamination, while the inventive compositions (Samples 6 and 7) does not show any delamination. In addition, it can be seen that Samples 6 and 7 show a much higher tear strength in the machine direction.

Example 3

In this example, the composition of the tie layers 104 and 108 and the composition of the core layer 106 are changed. Table 6 shows the composition of the comparative multilayered samples and those of the inventive samples. Table 7 shows the properties. Comparative film samples are identified with letters (See Samples G and I), while samples that exemplify the invention are identified with numerals (See Samples 8-10). These samples are produced in a similar manner to the samples of Example 1. The total film thickness is 5 mils.

TABLE 6 Layer 102/Layer Layer 104/Layer 102/104/106/108/110 110 108 Layer 106 (percentage of total Sample Structure (Outer layers) (Tie layers) (core layer) thickness) G 3 Layer ELITE 5100 No tie layer PP HA802H 40/20/40 8 5 Layer ELITE 5100 80% CBC2 + 20% PP HA802H 35/5/20/5/35 ENGAGE 8100 9 5 Layer ELITE 5100 80% CBC2 +20% PP HA802H 35/5/20/5/35 VERSIFY 2200 I 3 Layer ELITE 5100 No tie layer 80% PP HA802H + 20% 40/20/40 ENGAGE 8100 10  5 Layer ELITE 5100 CBC2 80% PP HA802H + 20% 35/5/20/5/35 ENGAGE 8100

The properties are shown in the Table 7.

TABLE 7 Dart 1% MD 2% MD MD A Sec Mod Sec Mod tear Heat seal fail Sample (g) (psi) (psi) (g) mode G 883 73822 57381 1485 Delamination 8 967 70935 56905 2024 No Delamination 9 874 74780 58564 2176 No Delamination I 1150 60564 46834 1404 No Delamination 10  1000 64953 50206 2238 No Delamination

As can be seen from the Table 7, the comparative sample G shows delamination, while comparative samples 8-10 show no delamination. Compared to comparative Examples G, inventive Examples 8 and 9 shows significantly improved MD tear at equivalent modulus while overcoming the delamination issue observed in Example G. Inventive Example 10 demonstrates superior MD tear with excellent modulus as compared to Example I.

Example 4

In this example, the outer layers 102 and 110, the tie layers 104 and 108, and the core layer 106 all utilized different compositions from those in the Examples 1-3. The compositions are shown in the Table 8A. The layer structure for inventive samples 11-12 are tabulated in Table 8A. The multilayer film has a total thickness of 4.25 mils. Inventive samples 11 and 12 show higher MD tear and higher modulus as compared to an all polyethylene 5 layer structure (Sample J).

TABLE 8A Layer 102/Layer Layer 104/Layer 102/104/106/108/110 110 108 Layer 106 (percentage of total Sample Structure (Outer layers) (Tie layers) (core layer) thickness) 11 5 Layer ELITE 5100 + CBC1 80% HA802H + 35/5/20/5/35 10% LDPE 133A 20% ENGAGE 8100 12 5 Layer ELITE 5100 + CBC1 PP H-110 35/5/20/5/35 10% LDPE 133A

Samples 11-12 (inventive samples) are prepared on an Alpine 7-layer blown film line. The diameter of the extrusion die is 200 mm and die gap is 2 mm. The die output is 12.13 lb per inch die circumference. The total throughput is 350 lb per hour. The blow-up ratio (BUR) is 1.73 and draw down ratio was 9.09. The total film thickness of 4.25 mil is made. The line has 7 extruders. Extruders 1 and 2 and extruders and 6 and 7 were used for the outer (skin) layers 102 and 110, extruders 3 and 5 were used for tie layers 104 and 109, and extruder 4 for layer 106. Typical extruder temperature profiles are shown in Table 8B.

TABLE 8B Extruders Zones Temperature (° F.) (° C.) Extruders 1 and 2 Zone 1 Set point 70 21 Extruders 6 and 7 Zone 2-5 Set point 380 193 Zone 6-8 Set point 450 232 Extruders 3 and 5 Zone 1 Set point 70 21 Zone 2-5 Set point 380 193 Zone 6-7 Set point 450 232 Extruder 4 Zone 1 Set point 70 21 Zone 2-5 Set point 380 193 Zone 6-8 Set point 450 232 Die Set point 450 232

The properties are shown in the Table 9.

TABLE 9 CD CD MD MD 1% MD 2% MD Tensile Strain CD Tensile Strain MD Sec Sec Break at Stress at Break at Stress at Dart Mod Mod MD Stress Break Yield Stress Break Yield Example A (g) (psi) (psi) tear (g) (psi) (%) (psi) (psi) (%) (psi) 11 706 75571 59611 1611 5753 632 2385 6100 544 2491 12 610 78392 65113 1393 5543 645 2663 6057 561 2700

From the Table 9, it may be seen that samples having a polypropylene core layer show a significantly greater 2% secant modulus than the comparative samples which have a core layer that comprises polyethylene.

In summary, it may be seen that the use of a core layer that contains polypropylene performs significantly better than core layers that contain polyethylene. In addition, the use of tie layers that comprise a crystalline block copolymer composite to bond the core layer to the outer layers perform better than multilayer films that do not have elastomeric tie layers.

The inventive samples show no delamination in the heat seal fail test and display a machine direction tear of 850 to 2500 grams, specifically 1000 to 2300 grams when tested as per ASTM D 1922, and display a 2% machine direction modulus greater than 50000 psi when tested as per ASTM D 882. The multilayered film may be used to produce articles. The articles include bags for transporting large quantities of commercial goods, foods, grains, and the like. 

What is claimed is:
 1. A multilayer film comprising: two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer.
 2. The multilayer film of claim 1, where the polyethylene comprises a linear low density polyethylene or an ethylene-α-olefin copolymer.
 3. The multilayer film of claim 2, where the linear low density polyethylene in each outer layer has a melt index I₂ of 0.25 to 2.5 g/10 minutes when measured as per ASTM D 1238 at 190° C. and 2.16 kg.
 4. The multilayer film of claim 2, where the ethylene-α-olefin copolymer is ethylene/propylene, ethylene/butene, ethylene/1-hexene, ethylene/1-octene, ethylene/styrene, ethylene/propylene/1-octene, ethylene/propylene/butene, ethylene/butene/1-octene, ethylene/butene/styrene, or a combination comprising at least one of the foregoing ethylene-α-olefin copolymers.
 5. The multilayer film of claim 3, where the outer layer further comprises low density polyethylene and/or high density polyethylene.
 6. The multilayer film of claim 4, where the outer layer further comprises low density polyethylene and/or high density polyethylene.
 7. The multilayer film of claim 1, where the crystalline block copolymer composite comprises a crystalline ethylene based polymer, a crystalline alpha-olefin based polymer, and a block copolymer comprising a crystalline ethylene block and a crystalline alpha-olefin block, wherein the crystalline ethylene block of the block copolymer is the same composition as the crystalline ethylene based polymer in the block composite and the crystalline alpha-olefin block of the block copolymer is the same composition as the crystalline alpha-olefin based polymer of the block composite.
 8. The multilayer film of claim 1, where each tie layer further comprises an elastomer; and where the elastomer is a homogeneously branched ethylene-α-olefin copolymer, a polyolefin elastomer, a vinyl aromatic block copolymer, or a combination comprising at least one of the foregoing elastomers.
 9. The multilayer film of claim 8, where each tie layer further comprises polypropylene and/or polyethylene.
 10. The multilayer film of claim 1, where the polypropylene is selected from the groups consisting of random copolymer polypropylene, impact copolymer polypropylene, high impact polypropylene, high melt strength polypropylene, isotactic polypropylene, syndiotactic polypropylene, or a combination comprising at least one of the foregoing polypropylenes.
 11. The multilayer film of claim 10, where the core layer further comprises polyethylene or an elastomer; and where the elastomer is a homogeneously branched ethylene-α-olefin copolymer, a polyolefin elastomer, a vinyl aromatic block copolymer, or a combination comprising at least one of the foregoing elastomers.
 12. The multilayer film of claim 1, where the crystalline block composite has a melt flow ratio 0.1 to 30 dg/min, when measured as per ASTM D 1238 at 230° C. and 2.16 kilograms.
 13. The multilayer film of claim 1, where the crystalline block composite comprises 5 to 95 weight percent crystalline ethylene blocks and 95 to 5 wt percent crystalline alpha-olefin blocks.
 14. The multilayer film of claim 1, where the crystalline block composite has a crystalline block composite index of 0.3 to 1.0.
 15. An article comprising the multilayer film of claim
 1. 16. A method comprising: coextruding a multilayered film comprising: two outer layers; where each outer layer comprises polyethylene; two tie layers; where each tie layer comprises a crystalline block copolymer composite; where each tie layer has a first face and a second face that are opposed to each other, and where the first face of each tie layer contacts at least one outer layer; and a core layer; where the core layer comprises a polypropylene; where the second face of each tie layer contacts the core layer; and blowing the multilayered film.
 17. The method of claim 16, further comprising laminating the film in a roll mill. 